We proposed to study the details of the induction of crown gall tumors of plants by the soil bacterium Agrobacterium tumefaciens. A large plasmid of Agrobacterium, the Ti-plasmid, is responsible for oncogenicity and a specific part of this plasmid is found integrated in the host DNA of crown gall tumor cells. The specific aims are to investigate the organization of the DNA sequences in the plant genome which are sites of integration for Ti-plasmid DNA, and to study the expression of Ti-plasmid and plant sequences which are responsible for the tumorous state. The major techniques to be used are recombinant DNA methods, DNA sequence analysis, and DNA-DNA and/or DNA-RNA hybridization analysis. Specific fragments of DNA from plant tumors containing the boundaries between the plant DNA and the Ti-plasmid DNA will be isolated and cloned in bacteria (E. coli). We will determine the nucleotide sequence of the integration sites for Ti-plasmid DNA in the plant genome. These studies should reveal whether there are unique or multiple sites of integration and may provide structural information necessary for understanding the mechanism of DNA insertion. Furthermore, cloned DNA fragments will also be used as hybridization probes to detect the expression of relevant Ti-plasmid and plant sequences important in maintaining the tumorous state. These studies should provide significant information for understanding tumorigenesis in plants and for future experiments involving modification of Ti-plasmid as a vector for genetic engineering of plants.